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samuel_eng

15 Messages

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250 Points

Mon, Jan 4, 2016 8:22 PM

Ruckus AP capacity planning/formula

Ok,

CLIENTS: Single stream, 802.11ac

Connected to 5Ghz (only) and 20 channel width with theoretical and optimal RF conditions

AP: Single R500

How many concurrent clients can I serve with for example a Netflix 5mbps stream?

What is the formula / model?
Thanks

Question

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Updated 

5 years ago

20

8

Responses

oneofthemany

333 Messages

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5.1K Points

5 years ago

Example:

If your AP has a max TCP throughput of 40Mbps when using a 20MHz channel, this would put the AP at 100% of its airtime utilisation when the AP was passing 40Mbps.

To ensure that you dont overload your AP's, it is always best to work to capping the limits within your design to be using 75% of the AP's airtime utilisation.

This being the case your max TCP throughput value you should be aiming at the AP consuming is 30Mbps.

The simple math now is that if you divide 30 by 5 you get 6 clients.

Note: In this example this would mean that each client would need to be drawing a constant value of 5Mbps.

Now all you need to do is find out what the max TCP value is of a r500 when uising a 20MHz channel using a single stream - you can do this by conducting a FTP or iperf test.

Note: you will need to use more than 1 client to consume all of the available bandwidth and graph the network interface of the FTP/iperf server (I would use a linux machine for this as its more accurate)

I hope this answers you question.

Good Luck

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bill_burns

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3K Points

5 years ago

The short answer is "maybe 25" if you allow both bands to be used simultaneously.
(which is not the use case you described)

Keep reading if you want more detail.

I don't know what the "official" answer to this question is but since you're looking for a theoretical (pie in the sky) number:

I'd look at the info Ruckus provides for the AP:
http://www.ruckuswireless.com/products/access-points/zoneflex-indoor/zoneflex-r500

...ignore the 5Ghz max theoretical bandwidth (since you're specifying 20Mhz channelization) and substitute the 2.4Ghz figure of 300Mbps, divide by the 5mbps you specified, and arrive at a figure of 60 clients.

I would never expect to get close to "theoretical and optimal" performance, but since I'd configure my APs to support 40Mhz channelization (or more w/ ac support) and I'd expect some number of clients to support higher channelization and netflix should provide enough caching to smooth over momentary congestion issues...
Well... You're still not going to get close to that theoretical number.

BTW:
WiFi might not be your only bottleneck.
Do you have 300Mbps of internet connectivity?


Here are independent throughput results found on the Ruckus website:
http://www.ruckuswireless.com/carnet-performance-testing
If I'm reading it right, the effective throughput of an R500 (with 60 clients pulling traffic) drops to 80Mbps, leaving something better than 1Mbps per client.
If we use 80Mbps as our bandwidth cap, you get 16 netflix clients. (at 5Mbps each)
...but the "real world" nature of those results were disputed by other vendors.

Tom's Hardware claimed that a Ruckus ZF7363 delivered 111Mbps to 60 clients.
http://www.ruckuswireless.com/press/releases/20110718-independent-test-reveals-ruckus-outperforms-ot...

A more relevant test was conducted against a ZF7982:
http://www.ruckuswireless.com/press/releases/20130219-ruckus-smart-wi-fi-takes-top-marks-in-non-vend...
Their conclusion was that 25 iPad clients could simultaneously stream "HD" video through a single 7982.

So, compare the advertized performance numbers of a 7982 to those of the R500, scale the results appropriately and... you might get 10 or 12 simultaneous video clients per band.
I'm guessing, 'cause I didn't do the math there.
Plus, we totally lost track of your 20Mhz channelization specification.

The tests that Ruckus is highlighting seem to indicate that other brands would do worse.

..but feel free to search for your own throughput stress tests or conduct your own.

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samuel_eng

15 Messages

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250 Points

5 years ago

Thanks for your replies. I use 20Mhz channelization for frequency reuse on the 5Ghz.

Didi I get this right. If I go from 20->40 I can push more data to more clients? Is 20 "limiting" my AP's capacity as a whole?

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john_d

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Quite honestly, I wouldn't prematurely go 20MHz, unless your deployment is really so dense that you've got one AP on each channel from 36 to 161 all within earshot of each other and still need more capacity.

If you go from 20 to 40, you can push a higher bandwidth to each client, which may make them happier in terms of being able to achieve a higher bitrate/throughput at a greater distance, and that would hopefully get them off the channel faster.

I've found that in moderate density, 40MHz is still quite appropriate and even leads to more satisfied users, since they see bigger numbers when running a speed test, and you still get good air efficiency because clients get off the channel faster.

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5 years ago

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david_henderson

116 Messages

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2.3K Points

5 years ago

We just did some testing of a Ruckus R700 AP. We had 1080p video sitting on an internal server and used new MacBook Pros to connect. These laptops all had 802.11ac nics. We streamed this video to one client and then kept adding clients until we saw pausing or stuttering in the video. This was all using 20Mhz channel width and only 5GHz. Seven clients worked fine, as soon as we added the 8th video stream we got stuttering. Keep in mind that 1080p video is using more bandwidth than youtube videos unless they are HD and full screen If we used both bands I am guessing we could double the number of streams

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bill_burns

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Wow.

7 Macbook Pros w/ 802.11ac WiFi cards streaming 1080p video from an onsite server (so internet bandwidth/congestion wasn't factored in) through the 5Gig radio of an R700 w/ the channelization set to 20Mhz.

Not just a real world data point, but one that correlates very closely w/ the OP's use-case.

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5 years ago

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oneofthemany

333 Messages

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5.1K Points

Please replicate on 2.4Ghz and see what happens and r710 has no airtime fairness.

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5 years ago

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david_henderson

116 Messages

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2.3K Points

Unfortunately I do not have all the test gear any longer. We borrowed test gear from Aruba and Ruckus and did some extensive internal testing before deciding to go with Ruckus. All the test gear was returned. This summer we will be deploying 400 R710 APs. I hope that airtime fairness is working by then

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5 years ago

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john_d

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1080p video is generally defined to be around 8-10mbit bitrate... Getting ~56mbit of video throughput across 7 clients on a 20MHz channel seems like it's not too far fetched. My office uses, let's say, a Ruckus competitor's AP's that they prematurely locked to 20MHz because "high density" and I can barely pull 80mbit from it using a 1 client : 1 AP test.

If it's possible to get more than 7 clients to stream 1080p from a single AP at 20MHz, I'd be highly impressed. But at any rate, this is one of the reasons I was saying earlier that it's probably a mistake to prematurely decide to use 20MHz channels unless it's an extremely dense setup with 12+ overlapping AP's at a given point.

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5 years ago

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oneofthemany

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ATF by this summer..... wait for the tumbleweed :)

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5 years ago

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bill_burns

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5 years ago

Short answer:
Go for 40Mhz channelization (at least) in the 5Ghz spectrum.

You generally place APs close enough together to provide good 2.4Ghz coverage.
5Ghz spectrum does not propogate as well and there is more 5Ghz bandwidth available.

If you go for max bandwidth (channelization) on an AC capable AP, you've cut yourself down to 3 usable 5Ghz channels.
That's not any worse than the 2.4Ghz situation and (since 5Ghz signals don't propogate as far) you're still less likely to get interference in the 5Ghz band.
(assuming there are no 5Ghz cordless phones, etc.)

In general, I let the APs choose their channelization, and they go for the max that they're capable of.
I don't have many AC capable APs but so far I don't think this has caused me any problems.

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bill_burns

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oh... and yes, if a client is capable of connecting at 40Mhz channelization but doesn't because the AP is hard-coded to 20Mhz, then that client will go slower. (and consume more airtime) This leaves less airtime for the other clients, effectively slowing everyone down.

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5 years ago

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oneofthemany

333 Messages

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5.1K Points

This is dependant on band on the r500 until they fix airtime fairness on the 5GHz radio:


Here is Bill explaining Airtime Fairness:

http://www.ruckuswireless.com/asset/watch/276

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5 years ago

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david_henderson

116 Messages

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When is airtime fairness scheduled to be fixed in 5GHz?

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5 years ago

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john_d

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It's said to be 10.0. I have no idea when that will be released.

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5 years ago

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bill_burns

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I didn't realize that airtime fairness was missing from the R500. (at the current firmware release) This makes it much less suitable for streaming (downloading) video. (on 5Ghz)

Note: AFAIK: Airtime fairness applies to *downloaded* traffic.
All it takes is for one user to *upload* a large file to potentially monopolize "all" the airtime on a given channel.
I have not noticed Rucks (or any vendor) rate limiting client transmissions.

Most traffic is downstream so this usually isn't an issue but every once in a while this can kill WiFi performance.

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5 years ago

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samuel_eng

15 Messages

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250 Points

5 years ago

Ok, thanks for your advice. Keep in mind that chaning from 20->40 you lose 6dB per ch width doubling. That's half the distance.

But I can get my head around total AP capacity. Will channel width affect? Total net throughput if you compare 20 to 40?

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john_d

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Of course, halving the channel width from 40 to 20 will reduce each AP's capacity in half in terms of the net throughput. Even with the slight loss of SINR with creating wider channels, in practice a Ruckus AP will still deliver great 802.11ac speeds to a fairly large area. In my apartment, I can use 80MHz channels through 2 layers of drywall and still reach 300+mbit of observed throughput to a 3-stream laptop, which is *still* above the theoretical throughput of a 20MHz client.

If you are willing to double the number of AP's to support the effort to move from 40MHz to 20MHz, you can effectively still achieve the same net throughput,which would work fine for your Netflix scenario where clients need a relatively low peak throughput (in the 5 to 10mbit range for HD streaming) but many clients need it.

Like Bill said, in practice I've found that even for denser environments, wider 5GHz channels tend to work better than one would expect, because well-behaved clients tend to try to move a finite amount of data, and allowing them to do it twice as fast (or 4 times as fast for 80MHz channels) tends to get them off the air in a proportionally shorter time.

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5 years ago

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bill_burns

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as-per my above comment: Yes, increasing channelization will increase transmission speed. (to/from those clients that are able to support the higher channelization, and no "PHY" transmission speed change for other clients)

I'm not sure where the 6dB decrease you're talking about comes from but if you're concerned about decreasing the range of your 5Ghz connected clients, I'd expect them to be able to roam to the 2.4Ghz spectrum (which should still be at 20Mhz channelization) when they've gone beyond 5Ghz range.

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5 years ago

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oneofthemany

333 Messages

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5.1K Points

Excellent I get to use a car analogy :)

Think of the AP channel as a road where:

20MHz = Single Carriageway

40MHz = Dual Carriageway

80MHz = Motorway

Then think of the cars as packets, the more lanes you have the more cars and hence more packets, the more packets you can pass means you get more throughput.

In reference to your 6dB comment, I dont know where you have got this from, but it is incorrect.

All that happens when you double your channel size is that your Noise Floor increases by 3dB.

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5 years ago

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samuel_eng

15 Messages

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250 Points

Doubling channel width equals raising noise by 3dBm
http://www.wirelesstrainingsolutions.com/class/mod/forum/discuss.php?d=16

20 and 40 MHz have the same Tx Power, but 40 is less “concentrated”. That’s also 3dBm

3 dBm + 3 dBm = 6 dBm

6 dBm is according to Free Space Path Loss half the distance

Am I wrong?

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5 years ago

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samuel_eng

15 Messages

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250 Points

Found this as well:
http://alumni.cs.ucr.edu/~marslan/acorn-ton.pdf

"The 802.11n standard [1] mandates the use of the same maximum transmit power with and without wide channels. In an OFDM system, the transmit energy is uniformly distributed across the subcarriers. Since wide channels use 114 subcarriers and the total transmit power remains the same, the energy per subcarrier is theoretically reduced to 49% of that of 20 MHz bands (approximately halved). Expressed in dB, this translates to about a 3 dB reduction in the energy per sub-carrier."

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5 years ago

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bill_burns

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5 years ago

Oh... I didn't consider that Samuel might be trying to figure out how many 5Ghz APs he needs to support a certain number of "video" clients.

Samuel:
Are you aware of how many non-overlapping 40Mhz channels there are in the 5Ghz band?
I think it's 12.
https://en.wikipedia.org/wiki/List_of_WLAN_channels

How many clients do you need to support?
Would 12 channels be enough for your application?
(or 15, if you're allowed to use the 3 2.4Ghz 20Mhz channels and consume "all" spectrum for this one purpose)

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john_d

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5 years ago

One other point that came to mind: Don't forget that even if channel width is set to 40MHz, 20MHz rates are still in play. I routinely see my 80MHz capable units actively using 40MHz or 20MHz rates particularly close to the fringe of coverage. But of course, relying on this too much will result in poor spectrum efficiency, if you really are close to saturating all your 5GHz spectrum.

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